Description of problem:
If KMS is active, glyphs in fonts change their shape to solid rectangle which renders text unreadable. The change seems to be gradual and takes effect after several minutes of work in X. See attached screenshot.
If KMS is NOT active (nomodeset kernel parameter is set), this does not happen.
Version-Release number of selected component (if applicable):
kernel-2.6.27.7-130.fc10.x86_64
xorg-x11-server-common-1.5.3-5.fc10.x86_64
xorg-x11-drv-ati-6.9.0-59.fc10.x86_64
$ lspci | grep VGA
01:05.0 VGA compatible controller: ATI Technologies Inc RS690 [Radeon X1200 Series]
How reproducible:
100%, but I do not know exactly the action
Steps to Reproduce:
1. boot with KMS active (no kernel parameter added)
2. Browse the internet or otherwise use X applications.
3. Some glyps start to be rendered as solid rectangle and situation is gradually getting worse, still more and more glyphs become unreadable. Also, some icons disappear or get ugly/broken.
The font glyphs, pixmaps and icons should be rendered as intended.

The same bug shows up on my laptop, also with RS690. To reproduce it, I open Slashdot.org main page in Firefox and repeatedly zoom in, out and scroll. Still, it can take a few minutes.
I cannot reproduce it with kernel 2.6.27.5-123. I've seen it with 2.6.27.7-128.
From looking at the diff between the two versions, I started suspecting the GART sizing change in the radeon driver. Another hint is I'm getting 'Unable to use IGP GART table size 524288' in dmesg.
I am now testing a workaround: Adding the parameter 'gartsize=32' to radeon module. So far looks good.
I think I can see a bug in radeon_set_igpgart(). switch(dev_priv->gart_size) assumes the size is in megabytes, but it is in bytes. When it prints the error message, it attempts to fall back to 32 MB GART size, but I'm afraid the original size is still preserved in several variables. I'll test a patch and post it soon.

Created attachment 325233[details]
radeon: fix IGP GART size setting
I am now running with this patch instead of the workaround. The error message is gone. The black rectangles have not appeared yet. I'll let you know should they reappear.

Created attachment 325417[details]
screen corruption/tearing with nomodeset
Since I am not having suspend/resume (it worked every other time so far), I thought I'll try putting nomodeset back, without xorg.conf (i.e. EXA) - and I am getting screen corruption/tearing as shown.
xorg-x11-drv-ati-6.9.0-61.fc10
kernel-2.6.27.7-134.fc10
(this probably should be a separate bug, since this screenshot is about EXA+nomodeset - but I am just expressing my general frustration that switching between EXA/XAA, modeset/nomodeset, radeon/radeonhd, none really work happily.
The best for general usage - for me - is still XAA+nomodeset)

kernel-2.6.27.7-134.fc10 has been pushed to the Fedora 10 testing repository. If problems still persist, please make note of it in this bug report.
If you want to test the update, you can install it with
su -c 'yum --enablerepo=updates-testing update kernel'. You can provide feedback for this update here: http://admin.fedoraproject.org/updates/F10/FEDORA-2008-10772